ABSTRACT
Subjects fixated point targets in an otherwise dark room with monocular or binocular vision. Cyclovergence, or the difference between the torsional orientations of the eyes, depends on the head-centric distance and the elevation of the binocularly viewed target. This constraint on cyclovergence resembles the restriction that holds for the torsional position of a single eye which, according to Listing’s law, depends on the head-centric direction of the target. The law is valid for the viewing of distant targets that require no eye vergence. Patients with intermittent exotropia often suffer from double vision, because the eyes deviate outward during fatigue. The components of the rotation vectors represent the torsional, vertical and the horizontal component of the eye position. Opposite torsional movement of the two eyes changes the relative orientation of the retinal images. Such cyclovergence movements can bring regions in the image with disparate orientations in register.
